Like other posters, I have to agree that it might be too early to gauge the current level of success. While the U.S. has captured and killed many of the leaders of terrorism networks, more cells of those networks have sprung up in countries such as Yemen, and Pakistan has proved what many already knew--that they are not fully committed to a war on terrorism. Our relationship with them and several other countries is more tenuous that it was before the war.
However, the success of the war on terrorism depends on one's perspective. If you are Kurdish--like some of my students--then the war in Iraq freed them of a terrorist (Sadaam Hussein), and if you're a women living in Afghanistan, then you might also see the war on terrorism as freeing you from Taliban terror (of course, this is dependent on which part of Afghanistan you live in).
The problem with the word "success" is that the war on terrorism was not begun to free the Kurds or Afghan women from oppression; so those outcomes will most likely not be linked to the success or failure of the war.